The fusion of mouse myeloma cells with spleen cells from immunized mice (Kohler and Milstein, Nature (1975), 256, 496-497) was the first indication that it is possible to obtain continuous cell lines which produce homogenous (so-called "monoclonal") antibodies. Since then, a large number of attempts have been made to produce various hybrid cells (so-called "hybridomas") and to employ the antibodies formed by these cells for various scientific investigations (cf. Current Topics in Microbiology and Immunology, volume 81--"Lymphocyte Hybridomas", F. Melchers et al., Springer-Verlag (1978) and references therein; C. J. Barnstable et al., Cell, (1978), 14, 9-20; P. Parham, W. F. Bodmer, Nature (1978 ), 276, 397-399; Handbook of Experimental Immunology, 3rd edition, vol. 2, D. M. Wier, editor, Blackwell, 1978, Chapter 25, Chem. Eng. News, 15-17 (1979); Kennett, R. H., McKearn J. T., and Bechtol, K. B. (1980) Monoclonal Antibodies. Hybridomas: A New Dimension in Biological Analysis (Plenum, New York)). These reports describe the principal techniques for the production of monoclonal antibodies by hybridomas.
Monoclonal antibodies against human plasminogen activators (urokinase-type (u-PA) and tissue-type (t-PA)) and produced by hybridomas have been prepared and have been used for purification, identification, and immunochemical localization of the activators and their proenzymes (Kaltoft, K., Nielsen, L. S., Zeuthen, J., and Dan , K. (1982) Proc. Natl. Acad. Sci. USA, 79, 3720-3723; Nielsen, L. S., Hansen, J. G., Andreasen, P. A., Skriver, L., Dan , K., and Zeuthen, J. (1983) The EMBO Journal, 2, 115-119; Nielsen, L. S., Hansen, J. G., Skriver, L., Wilson, E. L., Kaltoft, K., Zeuthen, J., and Dan , K. (1982), Biochemistry, 21, 6410-6415; Dan , K., Dabelsteen, E., Nielsen, L. S., Kaltoft, K., Wilson, E. L., and Zeuthen, J. (1982), J. Histochem, Cytochem., 30, 1165-1170). Andreasen, P. A., Nielsen, L. S., Gr ndahl-Hansen, J., Skriver, L., Zeuthen, J., Stephens, R. W., and Dan , K. (1984), The EMBO Journal, 3, 51-56). It has recently been shown that inhibitors of plasminogen activators play an important role in the regulation of the plasmin mediated proteolysis. Such inhibitors have been identified in a variety of tissues, body fluids and cultured cell lines (Holmberg, L, Lecander, I., Persson, B., and .ANG.stedt, B. (1978), Biochim. Biopys. Acta, 544 128-137; Seifert, S. C. and Gelehrter, T. D. (1978) Proc. Natl. Acad. Sci. USA, 75, 6130-6133; Chmielewska, J., R.ang.nby, M., and Wiman, B. (1983 ) Thromb. Res., 31, 427-431; Emeis, J. J., Van Hindsbergh, V. W. M., Verheijen, J. H. and Wijngaards, G. (1983) Biochem. Biophys. Res. Commun., 110, 391-398; Golder, J. P. and Stephens, R. W. (1983) Eur. J. Biochem., 136, 517-522; Loskutoff, D. J., van Mourik, J. A., Erickson, L. A., and Lawrence, D. (1983), Proc. Natl. Acad. Sci. USA, 80, 2956-2960; Philips, M., Juul, A. -G., and Thorsen, S. (1984) Biochim. Biophys. Acta, 802, 99-110; Vassalli, J. -D., Dayer, J. -M., Wohlwend, A. and Belin, D. (1984)J. Exp. Med., 159, 1653-1668; Erickson, L. A., Ginsberg, M. H., and Loskutoff, D. J. (1984), J. Clin. Invest., 74, 1465-1472; Cwikel, B. J., Barouski-Miller, P. A., Coleman, P. L., and Gelehrter, T. D. (1984), J. Biol. Chem., 259, 6847-6851; .ANG.stedt, B., Lecanders, I., Brodin, T., Lundblad, A., and Low, K. (1985), Thrombos. Haemost., 53, 122-125; J. Biol. Chem. (1985), 260, 7029-7034). The mutual relationship of these inhibitors is at present not fully clarified, although recent evidence indicates that at least three immunologically dissimilar types of plasminogen activitor inhibitors exist. These include (1) protease nexin, (2) plasminogen activator inhibitor purified from placenta (.ANG.stedt, B., Lecander, I., Brodin, T., Lundblad, A., and Low, K., (1985) Thromb. Haemost. 53, 122-125), and (3) plasminogen activator inhibitors that inhibit u-PA and t-PA and which typically have been obtained from human endothelial cells, human blood platelets, and rat hepatoma cells (HTC), in the following referred to as endothelial type plasminogen activator inhibitor (e-PAI).
An inhibitor with remarkable similarities to e-PAI has been found in human plasma (Thorsen, S. and Philips, M. (1984) Biochim. Biophys. Acta 802, 111-118).
Monoclonal antibodies against placental plasminogen activator inhibitor have been prepared and such antibodies have been used for the purification of said inhibitor (.ANG.stedt, B., Lecander, I., Brodin, T., Lundblad, A., and Low, K., (1985) Thrombs. Haemost. 53, 122-125).